STEAM ENGINES 



391 



load as this, much of the time it is more economical to 

 use a smaller engine. 



538. Corliss-governed engines have a great many eo> 

 nomical advantages over other types of engines: (i) re^ 

 duced clearance volume, due to the proximity of the 

 valves to the cylinder; (2) separate valves for steam and 

 exhaust, the steam 



valves being on top and 

 the exhaust beneath, so 

 there is a free and short 

 passage for the water to 

 leave the cylinder; (3) 

 a wide opening of the 

 steam valve and a very 

 quick closing at cut-off, 

 thus giving a sharp point 

 of cut-off without wire 

 drawing; (4) the valve 

 mechanism permits of 

 independent adjustment 

 of admission and cut-off 

 release and compres- 

 sion. The disadvantages FIG. 276 DOUBLE-CYLINDER ENGINE 

 of this engine are that it 



is of necessity slow speed, and hence to get the required 

 power. must be large. This makes the first cost great, 

 not only in the engine itself, but in the material for an 

 engine room. 



539. A double-cylinder engine (Fig. 276), or a double 

 engine, as it is sometimes called, is an engine which has 

 two cylinders, both of which take the steam directly from 

 the boiler. Both cylinders of a double engine should be 

 connected to the same crank shaft, and their cranks 

 should be at an angle of 90 with each other. The only 



